import 'dart:math';

class GpsToGcj02 {
  static const double pi = 3.1415926535897932384626;
  static const double a = 6378245.0; // 地球长半轴
  static const double ee = 0.00669342162296594323; // 偏心率平方

  /// 判断是否在中国境内
  static bool _outOfChina(double lat, double lon) {
    if (lon < 72.004 || lon > 137.8347) return true;
    if (lat < 0.8293 || lat > 55.8271) return true;
    return false;
  }

  static double _transformLat(double x, double y) {
    double ret = -100.0 + 2.0 * x + 3.0 * y +
        0.2 * y * y +
        0.1 * x * y +
        0.2 * sqrt(x.abs());
    ret += (20.0 * sin(6.0 * x * pi) +
            20.0 * sin(2.0 * x * pi)) *
        2.0 / 3.0;
    ret += (20.0 * sin(y * pi) +
            40.0 * sin(y / 3.0 * pi)) *
        2.0 / 3.0;
    ret += (160.0 * sin(y / 12.0 * pi) +
            320 * sin(y * pi / 30.0)) *
        2.0 / 3.0;
    return ret;
  }

  static double _transformLon(double x, double y) {
    double ret = 300.0 + x + 2.0 * y +
        0.1 * x * x +
        0.1 * x * y +
        0.1 * sqrt(x.abs());
    ret += (20.0 * sin(6.0 * x * pi) +
            20.0 * sin(2.0 * x * pi)) *
        2.0 / 3.0;
    ret += (20.0 * sin(x * pi) +
            40.0 * sin(x / 3.0 * pi)) *
        2.0 / 3.0;
    ret += (150.0 * sin(x / 12.0 * pi) +
            300.0 * sin(x / 30.0 * pi)) *
        2.0 / 3.0;
    return ret;
  }

  /// GPS(WGS84) -> 高德(GCJ02)
  static List<double> gps84ToGcj02(double lat, double lon) {
    if (_outOfChina(lat, lon)) {
      // 不在中国，原值返回
      return [lat, lon];
    }
    double dLat = _transformLat(lon - 105.0, lat - 35.0);
    double dLon = _transformLon(lon - 105.0, lat - 35.0);
    double radLat = lat / 180.0 * pi;
    double magic = sin(radLat);
    magic = 1 - ee * magic * magic;
    double sqrtMagic = sqrt(magic);
    dLat = (dLat * 180.0) /
        ((a * (1 - ee)) / (magic * sqrtMagic) * pi);
    dLon = (dLon * 180.0) / (a / sqrtMagic * cos(radLat) * pi);
    double mgLat = lat + dLat;
    double mgLon = lon + dLon;
    return [mgLat, mgLon];
  }
}
